This invention relates to an improved apparatus and method for treating a moving web including textile and plastic webs with heated air by, in at least one oven zone, passing all of that zone's process air through a heat exchanger and discharging a portion thereof directly into an incinerator providing a source of heated air for the heat exchanger. Such portion is also cleaned by the incinerator and exhausted to atmosphere.
Common pollutants which are in the process air which should be removed are volatile organic chemicals, including knitting oils and other finishes and impurities related to textile, plastic and other webs or other being treated.
Heretofore, oven exhaust has been cleaned of pollutants by either central precipitators, scrubbers or incinerators external to the oven.
Precipitators and scrubbers have been difficult to maintain. The polluted air must be cooled, with the result that the pollutants condense in the air stream and onto any of the cooler surfaces. These contaminated surfaces must subsequently be cleaned and the condensed pollutants disposed of.
Central incinerators have been expensive to manufacture and install, and to operate. To reclaim the heat from the incinerated air stream, the heated air or water heated by an air to fluid heat exchanger, must be used in the plant. Frequently, excess heat may be produced and is wasted. Furthermore, if heated air is reintroduced into a well-balanced oven, that oven may require additional exhaust to maintain a balance with the room air. This added exhaust volume in turn increases the energy consumption and operating cost of the oven.
Prior attempts to solve the problems contemplated a heat exchanger and incineration system, both located externally to the oven. Subsequently, attempts were made in which exhaust air was passed through a burner and heat exchanger to heat circulating air. However, in this latter case, no attempt was made at incineration.
Accordingly, it is an important object of this invention to eliminate these problems by providing an incineration system which will be an integral part of the oven and whose heat will be used to heat the oven's circulating air, sometimes referred to as process air, all of which passes through a heat exchanger in a constant path back to the nozzles.
An important advantage of the invention resides in a reduction in energy consumption because no substantial amount of makeup air is added to the oven due to the incineration and heat exchanger system hereof and because most components are inside the oven where any heat lost is recaptured in the process. Further, as a result of controlling process temperature first by controlling the incineration temperature and then by utilizing a bypass carrying a portion of incinerated air past the heat exchanger should the process result in the incineration temperature falling below a predetermined temperature, the exhaust temperature and exhaust volume are minimized. Thus, energy costs are minimized.
As a further advantage, maintenance costs will be reduced since only clean incinerated air will enter one path of the heat exchanger. The system is easy to install since it is a modular part of the oven. Insulation will not be required for the incinerator, and insulation cost for the exhaust duct will be minimized since the exhaust temperature of exhaust air will have been reduced well below the its temperature upon incineration. Air entering the heat exchanger may be readily filtered.
Apparatus and method in accordance with the invention may be utilized with and adapted to a variety of ovens constructions including those illustrated in U.S. Pat. Nos. 4,295,284, 4,341,024 and 4,435,909.